[Fried_Guy]

Ok, so I got my engine assembled and running.

No vacuum leaks, oil leaks, smoke, smells, odd noises, overheating, surging, etc... the only problem is my idle quality.......I think .

Here's my combo:
406 SBC
5.7" Rods
9.1:1 compression ratio with 30cc dish KB pistons
670 Truck Avenger
Comp Cams Extreme 4x4 12-243-3 (270/278, 227/235, .480/.498, 111)
IE 200cc heads with the exhaust cleaned up
high performance ignition system
fully balanced and blueprinted
All new parts except for the block (which has been thoroughly worked on)
all the bells and whistles, etc, etc, etc.

I can get it to idle at around 800RPM in neutral, but it's not the smoothest idle. Pulls 16"-17" of vacuum in neutral. Haven't checked it in gear.

Messed with the timing a bunch... doesn't seem to have much of an affect after around 18 degrees. Using vacuum advance on full source.

I tuned my idle mixtures properly... but they seem a little off. They really have almost no affect on the vacuum or idle quality unless I lean them out too much and it stalls. On most of the other engines I've worked on, adjusting the idle mixture screws seems to make a significant change in the vacuum. It seems that with this setup it's either too lean, or ok. No in between.

The vacuum seems good, but doesn't the idle speed seem a tad high?

Here's the only problems I can see:
1. I converted a dead head regulator into a flow through
-at idle the pressure fluctuates rapidly between 3-5psi
2. Using stock exhaust system
-don't know if it's clogged or how restrictive it is
3. Carb problems
-needs to be cleaned/modified?
4. I'm totally trippin'
-this is to be expected with the combo....

Any input would be great
Thanks in advance,
Casey

Oh, and this isn't for a chevelle sadly to say... it's for my 77 blazer all purpose 4x4

 

[SS402]

Hello Casey, right off the bat i'd say you need more carburetor, 750cfm would be the minimum with that combo.. 3-5psi is not enough to maintain correct fuel level.. check and adjust the float level.. what size are the chambers on those heads..? use a vacuum gauge and adjust the initial until highest vacuum is reached then readjust the idle speed and air-screws.. double check and make sure there are no vacuum leaks.. is the vacuum advance hooked up to manifold or ported vacum.. ? what distributor are you using and how is the centrifugal advance setup..? start with that and keep us posted

 

[Fried_Guy]

This is not a revving motor... should hit rev limiter at 5750 RPM.

It'll rev to the moon since all the parts are good and i'm using 3/8" pushrods and magnum roller rockers etc etc etc.

Going by the old formula (CID * RPM / 3456 * VE)...
406 * 5750 / 3456 * .9 = 608CFM
I know this is just a formula, but I'd rather go low then high... and I doubt my engine has a VE of .9

Would a 750 make it IDLE better?

Floats were on, 64cc chambers (9.1:1 CR), 18 degrees advance gives best vacuum, air screws still do nothing really to change vacuum level, no vacuum leaks, vac advance on full manifold vacuum, mallory 85 HEI distributor with high vibration mallory hifyre VI-AL ignition box, mech curve should start at 1000 and end around 3000 for about 36 total.

 

[wotr]

It is not the size of your carb. Should idle good with even a 2 barrel. I have run a 400sb with a 600cfm vacuum carb and it would idle good and run good at the track. I would put it in gear to tune it . When you put it in gear the idle will be lower and you may have to richen it more than in neutral for it to idle in gear. I would move the timing around in gear also. I have run as much as 30 initial with vacuum. Carb could be dirty, check your air bleeds. LJ

 

[Fried_Guy]

Quite possibly a dirty carb... sat in the garage for a bit before I stuck it on. I'll clean it up and blow it out and see if that helps any.

It's funny you say tune it in gear... I was about to do that, and then I ran out of gas... so the moment I put in in gear (for the first time since I've build the engine) it died! and it was dark so I didn't get any more gas for it since I couldn't work on it. I work quite a while away from where I live so I stay near my work during the week and I only go home Monday and Tuesday (days I'm off). I'll check all that out on Monday.

Anything blatently wrong with the combo or anything stand out like a sore thumb?

 

[novaderrik]

the idle mixture screws don't seem to be working becasue the primary throttle shaft is opened too far and the transfer slots are exposed.
make sure the choke is all the way open and the fast idle cam is totally disengaged before playing with the mixture screws. it's also possible that your throttle cable is holding it open a bit- sometimes the bracket or gas pedal needs to be tweaked a little bit to allow the primaries to totally close, but it can be checked by starting the car and unhooking the throttle linkage- it if idles down, you've found your problem.

 

[wotr]

"I tuned my idle mixtures properly... but they seem a little off. They really have almost no affect on the vacuum or idle quality unless I lean them out too much and it stalls"



He said he leans it out and it stalls,, wouldn't stall if it is idling on the transfer slots. LJ

 

[Fried_Guy]

The transfer slot shouldn't be exposed excessively, it's not on my fast idle cam, the engine is fully warmed up off of the choke, and the linkage isn't hooked up when I tune the carb.

I can adjust the idle speed no problem... but under 800 it's very rough, and lower than 750 just won't start or run at all.

When I get home Monday I'll clean the carb and make sure my needles are seating properly and my air bleeds are clean, make sure the transfer slot exposed is about square and not excessive, i'll try to get my hands on another regulator so I get steady fuel flow to the carb, check again for vacuum leaks, then i'll time the engine and tune the carb for the best vacuum.

This seems fuel related to me... like it's not atomizing at low RPM good enough.

Do you think that opening my secondaries a bit more will help?

Thanks a lot guys,
any other suggestions?

 

[novaderrik]

"I tuned my idle mixtures properly... but they seem a little off. They really have almost no affect on the vacuum or idle quality unless I lean them out too much and it stalls"



He said he leans it out and it stalls,, wouldn't stall if it is idling on the transfer slots. LJ

i saw that, and i've had times when i couldn't get the idle screws to do much besides make the engine die if i went too far one way or the other and it just dies or starts running rough. usually closing the throttle blades a bit has helped.


but the best way to get an engine to start up nice and idle nice and smooth is to get a quadrajet instead of a Holley, but i won't go there...

 

[Fried_Guy]

That's why I asked if opening my secondaries a bit would help

and it's probably best to use a q-jet on anything that needs low end... i put one on my dad's 350 custom deluxe 30 and it sips gas with a nice low idle... but I understand the workings of the holley better believe it or not. Plus this carb should function better offroad without additional mods